You can see how much motion is detected in the Motion meter at the top of the view. Slider the trigger to the level of activity you would like to trigger recording. Videos are saved to '~/Movies/OnCue'. Press 'Arm' to start a countdown. When the countdown reaches 0, the motion detection is active and any motion above the level set in the trigger will begin recording.
At the bottom of the popover, the left option can be selected to keep the popover window open. Preview will open a window to show what the camera sees and will highlight motion in red. On the right is a button for the preferences dropdown where you can select options, view the about window, or close the app.
Preferences include opening the preview window at launch and setting the recording time out in seconds. This is how long a recording will last past the last triggering motion that was detected.